The measurement of the intraocular pressure is an important diagnostic tool for the identification of eye disorders, especially glaucoma. Tonometry is routinely used to screen the population at large and to track persons with known pathology. For more than two decades, the Goldmann tonometer has been a standard in the art of tonometry. See U.S. Pat. No. 3,070,997 patented Jan. 1, 1963.
Using the Goldmann apparatus, the intraocular pressure is measured by flattening or applanating a standard area of the cornea to conform to a planar corneal contact surface of a corneal applanation device placed in contact with the cornea. This method, known as applanation tonometry, employs a circular transparent plane surface, or corneal contact surface, of known diameter which is urged against the cornea while an observer views the degree of applanation of the cornea through the corneal contact surface with the aid of a slit lamp or similar light source and a small quantity of fluorescein placed in the lacrimal fluid. The medical observer adjusts the force applied to the corneal contact surface until the applanated area of the cornea just conforms to a predetermined standard area defined by the corneal contact surface, at which point the force urging the surface against the cornea and determining the intraocular pressure is recorded.
In the prior art devices, the corneal contact surface must be sterilized for each use. This is desirable because infection and disease may possibly be transmitted through lacrimal fluid, and each measurement of the intraocular pressure requires that the corneal contact surface be brought into physical contact with the cornea for an interval ranging from a few seconds to a minute or more. A disadvantage of the prior art tonometers was that the corneal applanation device including the corneal contact surface had to be physically removed from the tonometer after each use for sterilization.
Other patents describing various applanation tonometers are U.S. Pat. Nos. 4,621,644; 4,624,235 and 4,628,938.